Your lab report says arsenic above 0.010 mg/L, or nitrate above 10 mg/L. A whole-house filter will not touch either one, and the best reverse osmosis system for well water is the usual answer for the kitchen tap. RO pushes water through a membrane to catch dissolved contaminants, and you install it under the sink to cover drinking and cooking water.
It has costs: it wastes water, it needs enough pressure to work, and it is not a disinfectant. This guide compares four real under-sink systems on the specs their makers publish, so you can match one to your report instead of a marketing percentage.
Our pick: iSpring RCC7AK, a six-stage 75 GPD system certified to NSF/ANSI 58 per iSpring, with a final alkaline remineralization stage, for about $240. Want to pay less? The Express Water RO5DX costs about $190, and the APEC ROES-50 lists a 2,000 ppm TDS limit and 40-85 psi feed pressure. RO does not disinfect, so a positive coliform test means shock chlorination and UV first. For arsenic, ask your lab which form you have, because RO removes arsenic V far better than arsenic III.
iSpring RCC7AK 6-Stage Alkaline Reverse Osmosis System
iSpring lists six stages: sediment, GAC, carbon block, the RO membrane, a fine GAC polishing filter and an alkaline remineralization filter, at 75 GPD and certified to NSF/ANSI 58. It adds a mineral stage for taste, which plain RO lacks, and costs about $10 more than the RCC7. It carries a 1-year limited warranty with lifetime technical support.
Check today's price →Quick comparison
| Product | Best for | Key detail | Price |
|---|---|---|---|
| iSpring RCC7AK | Arsenic or nitrate at the tap, better-tasting water | 6 stages, 75 GPD, NSF/ANSI 58, alkaline remineralization, 25 lbs | about $240 |
| iSpring RCC7 | Same RO core, no mineral stage | 5 stages, 75 GPD, 3.2 gal tank, NSF/ANSI 58, 1:3 pure to drain | about $230 |
| Express Water RO5DX | Lowest price, simple setup | 5 stages, 50 GPD, 3-4 gal waste per gal, 31 lbs, 1-year warranty | about $190 |
| APEC ROES-50 | High-TDS wells, published feed limits | 5 stages, 50 GPD at 60 psi, 2,000 ppm max TDS, 40-85 psi feed | about $230 |
Our picks, one by one
iSpring RCC7AKBest overall
iSpring lists a 0.0001 micron RO membrane, 75 GPD, NSF/ANSI 58 certification, dimensions of 15.5 x 5.1 x 19 inches and a weight of 25 lbs. The sixth stage adds minerals back and neutralizes the slightly acidic RO water. iSpring prices it at $239.99, with a 30-day return policy. Choose it over the RCC7 if flat-tasting RO water bothers you; skip it if you want the cheapest system.
Check price & availability →iSpring RCC7Best value 75 GPD
iSpring lists five stages (PP sediment, GAC, carbon block, RO membrane, post-carbon), 75 GPD, a 3.2-gallon tank, NSF/ANSI 58 and a feed TDS limit under 2,000 ppm. The maker rates drain at 1:3 pure to drain with the tank. Pre-filters change every 6 to 12 months and the membrane every 2 to 3 years. At $229.99 it is the same RO core as the RCC7AK, so pick it only if you do not want the mineral stage.
Check price & availability →Express Water RO5DXBest budget
Express Water lists the RO5DX at $189.99 with a 1-year warranty, 17 x 15 x 5 inch dimensions, about 31 lbs, and 3 to 4 gallons of wastewater per gallon of pure water. The Amazon listing says 50 GPD, a 4-gallon tank and NSF 58 and 372; the Express page does not name the standards, so confirm in the NSF database. It costs about $40 less than the APEC and gives up published feed limits in exchange. Pick it for a clean-tasting, low-cost start, not for a high-TDS well.
Check price & availability →APEC ROES-50Best published feed limits
APEC lists 50 GPD at 60 psi and 77°F, 30 GPD at 50 psi, a 4-gallon tank, 40-85 psi feed pressure, 40-100°F, pH 2 to 11, and a 2,000 ppm maximum TDS. It uses a sediment filter, two carbon blocks, a TFC membrane and a coconut shell polishing filter. At $230.99 it costs about $40 more than the Express, but you get the numbers in writing. Pick it if your pressure sits near 40-60 psi and your TDS is high.
Check price & availability →How we chose
This is a researched guide, not a product test. We read the maker pages for the iSpring RCC7AK and RCC7, the Express Water RO5DX and the APEC ROES-50, plus Connecticut's health department guidance on arsenic in private wells. We kept systems with a published GPD and a certification statement, sold on Amazon.com. Where a maker did not publish a number, we left it out. We named an NSF/ANSI standard only when the maker lists it.
- GPD at a stated pressure: output means little without it.
- Feed limits: TDS ceiling, pressure window and temperature.
- Certification: NSF/ANSI 58 or WQA Gold Seal, as listed.
- Waste rate and upkeep: drain ratio, filter schedule and warranty.
Do you need RO? Match the report
Test first at a state-certified lab, and retest yearly. EPA and CDC both say to test private wells annually for coliform, nitrate, TDS and pH. Then read your result:
- Arsenic above 0.010 mg/L: RO is a point-of-use option. Connecticut's health department says RO removes 60 to 65 percent of arsenic III and 95 to 98 percent of arsenic V. Ask the lab which form you have, or pre-oxidize.
- Nitrate above 10 mg/L: RO is a common point-of-use fix. Test the treated water, because performance varies by system.
- High TDS: RO lowers it, within each system's feed limit (2,000 ppm for the APEC and the iSpring RCC7).
- Coliform positive: RO is not a disinfectant. Shock chlorinate, retest and use UV. Our UV guide covers it.
- Orange stains, scale or rotten egg smell: treat those first, because they foul an RO membrane. See our rotten egg guide.
Our well testing guide shows which test to order.
The arsenic form matters
Connecticut's health department explains that arsenic III has no charge and arsenic V carries a negative charge, which is why RO catches arsenic V better. It says pre-oxidation with an oxidizer can convert arsenic III to arsenic V ahead of an RO unit.
That matters for your purchase. If your lab reports total arsenic only, you do not know which form you have. Ask for speciation, or plan a treated-water retest. Connecticut recommends testing treated water annually to verify the system works, and retesting every five years once arsenic is detected. Chlorine pre-oxidation changes your install, so a water treatment pro should design it.
Speed, pressure and the waste-water bill
Two numbers decide whether RO feels fast: GPD and the pressure feeding it. A typical private well runs a pressure switch around 40 to 60 psi, so check yours against each system's window (APEC lists 40-85 psi).
| System | Rated GPD | Hours to make 4 gallons |
|---|---|---|
| iSpring RCC7AK / RCC7 | 75 | about 1.3 |
| Express RO5DX / APEC at 60 psi | 50 | about 1.9 |
| APEC at 50 psi | 30 | about 3.2 |
Formula: hours = 4 gallons / GPD x 24. GPD ratings assume the maker's test pressure. APEC publishes 30 GPD at 50 psi, so weak pressure slows you down.
RO also sends most of the water down the drain, which matters if you have a limited pump or a small septic field.
| RO water per day | Waste at 3:1 | Waste at 4:1 | Waste per year (3:1 to 4:1) |
|---|---|---|---|
| 1 gal | 3 gal | 4 gal | 1,095 to 1,460 gal |
| 2 gal | 6 gal | 8 gal | 2,190 to 2,920 gal |
| 4 gal | 12 gal | 16 gal | 4,380 to 5,840 gal |
Formula: waste per day = RO gallons x ratio; per year = x 365. Connecticut's health department and Express Water both cite 3 to 4 gallons of waste per gallon treated. For a well on a septic system, it all goes to the drain. Your actual ratio depends on pressure.
Install and upkeep
An under-sink RO connects to the cold line, a dedicated faucet and a drain saddle. Most are a weekend DIY job. Hire a licensed plumber if you are unsure about the drain connection or your pressure. iSpring lists pre-filter changes every 6 to 12 months and the membrane every 2 to 3 years for the RCC7. Sanitize and flush new filters as the manual says.
Keep a simple log: install date, filter change dates and the date of each treated-water lab test. When the membrane ages, output drops and the dissolved solids in the tap water rise, so a yearly lab test is the honest check. A cheap handheld TDS meter can show a trend between lab tests, but it measures total dissolved solids only. It cannot tell you arsenic or nitrate.
If your pressure is low, iSpring sells a pump version (RCC7P). Put the RO after your sediment and iron treatment. Our treatment order guide explains the sequence.
Reading the certification claims
iSpring lists NSF/ANSI 58 for both the RCC7AK and the RCC7. That standard covers reverse osmosis drinking water systems, and you can check it in the NSF database by company and model. APEC's own page says WQA Gold Seal for TDS reduction and lists no NSF/ANSI numbers, although the Amazon listing mentions NSF 58 and 372. Express Water's page names no standard either. Treat marketing figures like "99.99 percent" as the maker's claim, not as proof for your well.
Certification also says nothing about arsenic III or nitrate at your specific levels. The only proof is a lab test of the treated water, which is why every article in this cluster ends with a retest.
Plan the sink before you order
Measure the cabinet. iSpring lists the RCC7AK at 15.5 x 5.1 x 19 inches and 25 lbs, the Express RO5DX is 17 x 15 x 5 inches and about 31 lbs, and APEC lists the ROES-50 at 15.5 x 5.25 x 17 inches with an 11 x 11 x 15 inch tank. The tank sits beside it. You also need a hole for the dedicated faucet, a cold-water tap point and a drain connection.
If you rent the house, or the sink is granite, ask a plumber about the faucet hole first. Pick a spot where you can reach the filters, because pre-filters change at least once a year.
What the mineral stage does
RO membranes strip dissolved minerals, so the water can taste flat. The iSpring RCC7AK adds a mineral stage after the membrane, which iSpring says restores minerals and neutralizes pH. The Express RO5DX and APEC ROES-50 do not include a mineral stage. It is a taste choice, not a safety feature, so do not pay for it if you only want arsenic or nitrate reduction.
After install, flush the system and discard the first tank as the manual says. Then take a treated-water sample to a certified lab so your report shows the real result.
Who should not buy RO
- Coliform positive and nothing else: you need disinfection, not a membrane.
- Hard water only: a softener is the right tool. See our softener guide.
- Pressure under 40 psi: fix the pump or add a booster first.
- You expect whole-house RO: these are single-tap systems. A whole-house setup is a different, expensive job for a contractor.
Frequently asked questions
Does reverse osmosis remove arsenic from well water?
Yes, in part. Connecticut's health department says RO removes 60 to 65 percent of arsenic III and 95 to 98 percent of arsenic V. Ask your lab which form you have, and test the treated water after install.
Can reverse osmosis make well water safe from bacteria?
No. RO is not a disinfectant, and a positive coliform test means shock chlorination and a retest, then UV for ongoing protection. Use RO for dissolved contaminants like arsenic, nitrate and TDS.
How much water does an RO system waste?
Connecticut's health department and Express Water both cite 3 to 4 gallons of wastewater per gallon of treated water. iSpring lists 1:3 pure to drain for the RCC7. At 2 gallons of RO water a day, that is about 2,190 to 2,920 gallons of waste a year.
What water pressure does an under-sink RO need?
APEC lists 40-85 psi for the ROES-50 and 50 GPD at 60 psi, dropping to 30 GPD at 50 psi. Most private wells run around 40 to 60 psi, so check your switch setting.
How often do RO filters need changing?
iSpring lists 6 to 12 months for the RCC7 pre-filters and post-carbon, and 2 to 3 years for the membrane. A gritty or high-TDS well wears them faster, so retest the treated water yearly.
Prices are approximate and change often. Contains affiliate links; we may earn a small commission at no extra cost to you.